docs: def ses_ratio(self):
          """
          The ratio
  
          risk_investigation_time / investigation_time / ses_per_logic_tree_path
          """
          if self.investigation_time is None:
              raise ValueError('Missing investigation_time in the .ini file')
          return (self.risk_investigation_time or self.investigation_time) / (
              self.investigation_time * self.ses_per_logic_tree_path)